The present invention relates generally to furnaces for processing expandable ores such as vermiculite, perlite and the like. More particularly, the present invention relates to a preheater-equipped furnace adapted for use with a variety of expandable ores.
Vermiculite includes a group of hydrous silicates of various metals such as aluminum, magnesium and iron. Perlite is a siliceous, valcanic glass material primarily consisting of oxides of silicate and aluminum and combined water. These materials may be expanded through heat processing with an appropriate high temperature furnace, operating at a temperature in the order of 2500 degrees fahrenheit. When perlite, for example, is properly heat processed, it may expand up to twenty times its original volume, resulting in decreased density. In their expanded form these materials are of value as insulation products, and a variety of other well known applications are of commercial importance.
In the prior art a variety of furnaces have been proposed for heating such expandable minerals. Usually the incoming raw ore may be dropped through suitable ports providing access interiorly of a furnace tube, whereupon raw ore will drop downwardly towards an external blast nozzle. The extreme heat generated within the furnace will expand the ore, and the combination of resultant lower product density and upward directed gas pressure will propel the expanded product out from the furnace. Subsequently, the product may be conveyed to a typical cyclone separator which cools and separates the expanded ore from hot waste gases.
For energy efficiency it will be appreciated that in certain circumstances suitable preheating of incoming raw ore may be necessary. However, preheating requirements differ with various ores. For example, for efficient operation perlite should be preheated. Vermiculite generally does not require preheating.
Often preheating is accomplished in a separate rotary heater. However, separate preheating structure in fluid flow communication with a furnace input chamber has been suggested and disclosed in U.S. Pat. No. 3,097,832 issued to Murdock July 16, 1963. A preheating system involving a plurality of, vertically spaced-apart, inclined interiorly mounted baffles is shown in U.S. Pat. No. 3,311,358. In the latter device ore is dropped through a preheating chamber, dropping from one baffle plate to the next in succession. Other prior art patents broadly relevant to the present invention include U.S. Pat. Nos. 3,447,789; 3,206,905; and 2,978,339.
As will be appreciated by those skilled in the art, the frictional characteristics of raw perlite ore can result in severe wear and eventual destruction of critical furnace components. The latter factor is further aggravated by the extreme temperatures necessary for suitable processing. Normal wear and tear experienced because of friction in prior art devices usually results in periodic down time, mandating repair. Because of the high temperature at which such apparatus operates, several hours must be expended to allow the machinery to cool to permit maintenance. Thus an improved system for facilitating preheating while permitting eased maintenance and repair is mandated. Moreover, because of the wide variety of minerals ores with which such furnaces may be employed, it is imperative that, if the system is to operate economically, the equipment be adapted to be readily modified for processing ores of different types.
A further problem with prior art devices is that certain mineral impurities and heavy, unexpanded mineral elements may not expand properly during the process, and they will thus drop downwardly through the furnace tube. Resultant, potentially dangerous formations of waste material near the blast nozzle area may effect efficiency. Therefore it is desirable to provide a system wherein open flame injection may be employed at the bottom of a blast furnace tube which permits unobstructed gas flow, but results in improved control of unwanted unexpanded mineral waste.